Piston and cylinder assemblies have long been used in a variety of machines that provide repetitive linear motion. The repetitive linear motion is caused by a piston rod moving between an extended and a retracted position. The piston rod is moved by reciprocating motion of the attached piston within the cylinder. The piston is moved by controlled pneumatic or fluid pressure exerted against the piston to move the piston rod with respect to the cylinder.
Various linkages or tools may be mounted onto the piston rod. Certain tools such as welding guns or clamps need to be rotationally affixed in a certain location. Consequently, certain cylinders and piston rods are equipped with an anti-rotation device to prevent the piston rod from rotating with respect to the cylinder. These devices may be in the form of a square piston rod extending through a complementary square hole in the cylinder head.
These type of non-rotatable piston and cylinder assemblies however cannot provide a leak proof seal or gasket about the square hole and square rod so the device cannot be double acting. A substitute return mechanism is often provided by the introduction of a compression spring positioned about the shaft above the piston and within the cylinder to return the piston and rod to the retracted position. The introduction of the spring adds extra complexity to the piston rod and further demands additional fluid pressure to overcome the continuous retracting bias of the spring.
Double acting cylinder and piston rod assemblies are often greatly desired because of the more precise and positive control for movement in both the extending and retracting directions. One does not merely rely on the biasing force of the spring for retraction but can more precisely and more forcefully retract the piston rod by having fluid pressure exerted on the top surface of the piston while the pressure is relieved on the bottom surface of the piston.
However, most double acting cylinder and piston rods do not have any anti-rotation device built therein and require additional exterior anti-rotation devices which add complexity and expense to the device. Some internal anti-rotation devices in the form of an interior splined shaft mounted in the cylinder are known. These interior splined shafts require special non-solid piston heads with a non-round hole machined therethrough.
What is needed is a double acting non-rotating piston and cylinder assembly that is made from standard pistons, rods, and cylinder components. What is also needed is an anti-rotation device that can be installed in the cylinder and mounted onto a standard piston and cylinder assembly about the piston rod to prevent the piston rod from rotating with respect to the cylinder.